The world's richest man claimed to be "absolutely serious" on Twitter about challenging the Russian President to a duel.
SpaceX founder Elon Musk listens at a press conference following the first launch of a SpaceX Falcon Heavy rocket at the Kennedy Space Center in Cape Canaveral, Florida, U.S., February 6, 2018.(photo credit: REUTERS)ByARIELLA MARSDENUpdated:
